Staged vapor-liquid operated ejector arrangement for multi-stage evaporator system



Sept. 23, 1969 E. F. STALCUP 3,468,761

STAGED VAPOR-LIQUID OPERATED EJECTOR ARRANGEMENT FOR MULTI-STAGE EVAPORA'I'OR SYSTEM Filed Sept. 2, 1966 FIG.|.

LOW PRESSURE 72 STEAM SUPPLY IMPURE PRODUCT OUT TREATMENT APPARATUS FIG.2.

LOW PRESSURE STEAM SUPPLY IMPURE' WATER OUT IMPURE WATER IN PRODUCT WITNESSES OUT INVENTOR z zzw Ernest F Stolcup BY 5 'w 5f United States Patent 3,468,761 STAGED VAPOR-LIQUID OPERATED EJECTOR ARRANGEMENT FOR MULTI-STAGE EVAPORA- TOR SYSTEM Ernest F. Stalcup, Lansdowne, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 2, 1966, Ser. No. 576,964 Int. Cl. C02b 1/06; B01d 3/06, 3/02 US. Cl. 202173 5 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an ejector arrangement for removing air and other non-condensible gases from a flash evaporator system, and particularly to a two stage vapor-liquid ejector arrangement employing liquid flow and heat exchange relationships in a unique and eflicient manner.

Presently, air removal equipment for water desalination systems usually comprises two stage, high pressure steam jet air ejectors made of stainless steel. With such systems, inter-after condensers are employed to condense the steam that would otherwise be lost with the air and other non-condensible gases removed from the system by venting to atmosphere. The inter-after condensers comprise shells, baffles, tubes and tube plates that are also fabricated from stainless steel materials in order to resist corroding and to withstand the forces attendant with the use of high pressure steam. The corroding of system components is particularly a problem with the use of pH control processes of the feed water. Such processes result in the formation of non-condensible gases and vapors that are naturally corrosive.

It is generally known that the first stage (high vacuum) ejectors can use low pressure steam, such as required for the brine or top heater, without a substantial increase in quantity of steam. It is the second (low vacuum) ejector which particularly requires the high pressure steam due to the fact that it must exhaust into the higher pressure atmosphere.

Briefly, in accordance with one aspect, the present invention describes a two stage ejector arrangement in which the suction chamber of a first ejector is connected in fluid communication with a flash evaporator designed to convert saline or other impure water into substantially pure water. Low pressure steam (already available at the site of the flash evaporator for heating the impure makeup water before it is flash evaporated) is fed into an actuating entrance portion of the ejector and exhausts into the suction chamber of a second, water actuated ejector. The low pressure steam passing through the first ejector draws or aspirates the air and other non-condensible gases from the flash evaporator and directs them, with the low pressure steam, to the second ejector.

The second ejector is actuated by a pressurized flow of liquid which comprises the water employed in the flash evaporator for flash evaporation. The water flows through the suction chamber of the second ejector where it produces an additional suction or aspirating force to assist removal of the steam and air exhausting from the first ejector. The water used to actuate the second ejector further serves to condense the steam drawn from the first ejector when it comes in contact therewith within the second ejector. The resulting condensate, along with the actuating water and the air and other non-condensible gases, exhaust into a water supply tank or container where the air and other gases exhaust to the atmosphere through a vent provided in the container. With the use of ejector actuating fluids that are readily available at the site of the flash evaporator, namely, low pressure steam and makeup water, the present disclosure describes a very effective and eflicient arrangement for withdrawing air and other non-condensible gases from a flash evaporator which is a primary object of the invention in an art (water desalination) where cost is a paramount concern.

Another aspect of the invention involves the unique employment of the supply container and a balanced, continuous flow of water therethrough to effectively preheat the makeup water for the flash evaporator system. The use of containers in ejector liquid recirculation arrangements is well known in the art. Such containers are used to store a supply of ejector actuating liquid and are provided with a venting port (for venting to atmospheric air and other non-condensible gases) and makeup liquid connection and drain outlet means for admitting and removing the ejector actuating liquid. With steam-water actuated ejector arrangements, the water passing through the water actuated ejector is naturally heated by the steam entering therein from the steam actuated ejector. This heat is passed onto the water within the container with the water entering therein from the ejector.

As well known, the makeup water directed to the flash evaporator must be heated before it enters the flash chambers for the flashing process, and this is generally accomplished with a separate water (top end) heater serially connected between the first flash chamber and its associated condenser. By eflectively using the heat inherently acquired by the water in the water actuated ejector to preheat the makeup water for the flash evaporator (in a manner to be more fully explained hereinafter) less work need be performed by the top end heater which forms generally another cost saving and primary object of the invention.

A further object of the invention is to provide an effective multi-stage ejector arrangement for a flash evaporator which eliminates the usual need for high pressure steam.

Yet another object of the invention is to provide an economical ejector arrangement for use in a corrosive environment, the ejector arrangement requiring only a low pressure vapor and a pressurized flow of liquid as the actuating fluids so that the component parts of the arrangement can be made of corrosive resistant materials other than stainless steel.

A more specific object of the invention is to provide a unique two stage ejector arrangement for flash evaporator desalting systems in which available low pressure steam is used to operate the ejector of the first stage, and flash evaporator makeup water is employed to operate the second stage.

Another more specific object of the invention is to provide a multi-stage ejector arrangement in which heat inherently acquired in at least one of the ejectors is transferred and effectively utilized by the use of a continuous flow of liquid to and from a container connected to receive the fluid output from the ejectors.

These and other objects of the invention will become more apparent from the following detailed description, taken in connection with the accompanying drawing, in which:

FIGURE 1 shows a schematic representation of one embodiment of the invention; and

FIG. 2 shows a schematic representation of a second embodiment of the invention.

Specifically, there is shown in FIG. 1 reference numerals 1, 2 and 3 diagrammatically representing three evaporation chambers of a multi-stage flash evaporator of the recirculating and regenerative heat exchange type. Chamber 1 is the first and highest pressure stage, 2 is the next highest and 3 is the final and lowest pressure stage, the number of stages (three) being given by way of example only. The chambers 1, 2 and 3 may be formed by a metal housing structure comprising a top wall 12, a bottom wall 13, vertical end walls 14 and 15, as well as front and rear walls (not shown), and vertical internal partitions 17 and 18 which cooperate with the wall structure to form the chambers. Chambers 1 to 3 are disposed in liquid communication with each other by way of interconnecting slots or orifices 21 and 22 formed in partitions 17 and 18 respectively, adjacent bottom wall -13. Chambers 1 to 3 are further disposed in fluid communication with each other by way of interconnecting slots or orifices 23 and 24 formed in the partitions 17 and 18, respectively, adjacent the top wall 12 for providing the lower and different respective pressure values in the chambers in a manner to be more fully explained hereinafter.

The housing structure further defines an equal plurality of vapor condensing spaces 25, 26 and 27 for receiving the condensible vapors formed in chambers 1 to 3 respectively. The condensing spaces are disposed in the uppermost portion of the housing structure and are further defined by generally horizontally extending trays 29, 30 and 31. The trays are provided with vertically extending vapor flow passages 33, 34 and 35 respectively, so that the vapors formed in chambers 1 to 3 may flow upwardly through the flow passages into condensing spaces 25, 26 and 27 respectively.

The vertical partitions 17 and 18 are further provided with apertures 36 and 37 immediately above the trays so that the falling condensate collected in tray 29 is free to flow through associated aperture 36 into tray 30 to join the condensate collected therein, and finally through aperture 37 into tray 31 for final collection and removal therefrom, as indicated by line 39, as product Water.

Condensing spaces 25, 26 and 27 are provided with suitable surface heat exchanging or condensing tube structures 41, 42 and 43 (only diagrammatically shown) for condensing the vapors that rise from the flash chambers into the condensing spaces. The inside of the condensing tube structures is generally known as the tube side and the proximate area outside the tube structure 41 to 43 is generally designated shell side.

Sea water, brackish water or other impure water from any suitable source, such as a river, lake or the sea, may be pressurized by a suitable pump (not shown) and directed through tube structure 43 (tube side), as indicated by line 46. The vapors rising from the flash chamber 3 heat the impure water directed through the condensing tube 43. The heated water is then directed from the condensing tube via line 44, and a portion thereof is rejected from the system and returned to the source in a well known manner and as indicated by line 47. The remaining and greater portion of the heated Water is directed through condensing tube structures 42 and 41, by branch line 47A, pump 45 and line 48 where it is further heated by the vapors rising from the flash chambers 2 and 1, respectively. The water is thus progressively heated in the tubes 42 and 41 before it is flash evaporated. The tubes 42 and 41 thus form heat recovery stages in the flash evaporator system whereas tube 43 represents a heat reject stage since it functions to reject at least a portion of the heat absorbed from the condensible vapors in the condensing space 27. As mentioned earlier, the number of stages is given by way of example only.

The impure water fed into the system via line 46 is generally termed makeup or feed liquid. After it is heated by absorbing the heat from the vapors in the condensing spaces 25 and 26, the impure makeup or feed water is then directed to a suitable top end heater 4? to which steam or other heated fluid is directed, as indicated by line 50. In the resulting heat exchange, the steam (if steam is used) is condensed and withdrawn as condensate through drain outlet, as shown by line 51, and the thus heated makeup is thence directed into the first flash chamber 1 as indicated by line 52. As the heated water for evaporation is directed into chamber 1, a portion thereof is flashed into vapor because of the reduced pressure ambient prevailing therein, and the vapor flashed therefrom rises upwardly, along with air and other non-condensible gases contained in the water, through flow passage 33, as indicated by dashed arrows 53, into condensing space 25. The vapor is condensed by heat transfer with the heat exchanging tube structure 41 and falls into tray 29 for collection. The air and non-condensible gases are withdrawn from the chamber 1 through the previously mentioned slot 23 provided in partition 17. The unflashed portion of the water flows through orifice 21 into the next and lower pressure stage chamber 2 wherein the same chain of events occur with the unflashed water thence flowing through orifice 22 into chamber 3 for final evaporation. The air and other gases are withdrawn from chamber 2 through slot 24 in partition 18 into chamber 3 where they join with the air and other gases liberated with the vapor flashed therein. From chamber 3 the air and gases are withdrawn in a unique manner to be more fully explained hereinafter. As the water flows through chambers 1, 2 and 3 with flash evaporation occurring, the water becomes more and more enriched with salts and other minerals and is termed enriched brine.

From the last and lowest pressure flash chamber (chamber 3 in FIG. 1), a portion of the enriched brine can be removed (blown down) from the flash evaporator 10 by a suitable pump and conduit as indicated by numerals 54 and 55, respectively. The remaining brine may be recirculated through the system as indicated by line 56. As well known in the art, the blowdown line is employed to remove from the system a portion of the enriched brine so that the water circulating through the system will not exceed a predetermined level of salinity.

A substantially pure water product is produced as a result of the flash evaporation and condensing functions performed respectively in the flash chambers and condensing spaces. As the rising vapors from the flash chambers 1 to 3 come into contact with the heat exchange tubes 41 to 43, the vapors condense thereon and fall from the tubes as condensate into trays 29 to 31. The pure water (condensate) flows towards the last tray 31 through the apertures 36 and 37 provided in the partitions 17 and 18. From the last tray 31, the pure water is withdrawn as the product liquid, as indicated by line 39, and directed from the system, as indicated by line 59, for storage and/or consumption. A suitable valve means 59A is provided in the line (conduit) 59 to control the flow of product water out of the system.

In accordance with the principles of the present invention, the descending order of pressure maintained'in flash chambers 1 to 3 is provided by a staged ejector arrangement generally designated 60 comprising two serially connected ejectors 61 and 62, with the ejector 61 being a low pressure steam operated or actuated device and ejector 62 being a liquid (water) actuated device. Structurally, the ejectors 61 and 62 comprise generally an entrance portion and suction creating nozzle means'generally designated 65 and 66, a suction chamber 67 and 68 and an exhaust or outlet portion 69 and 70 respectively. The suction chamber 67 of ejector 61 is connected to the flash evaporator for withdrawing air and other non-condensible gases therefrom as indicated by line 71. The entrance portion 65 of ejector 6-1 is connected to a suitable source of low pressure steam (not shown), which may be the source supplying the top heater 49, as indicated by line 72. The exhaust portion of the ejector 61 is connected in fluid communication with the suction chamber 68 of ejector 62, as indicated by line 73.

In the embodiment depicted in FIG. 1, the ejector 62 is actuated by a flow of water pressurized and directed to the entrance portion 66 of the ejector by a suitable pump 75, the intake of which is connected to a water supply container 76 by a suitable conduit means indicated by line 77. The pump 75 is further connected to receive a portion of the impure water from the line (conduit) 46 as indicated by branch line 78. The water in the container is held at a predetermined level to provide an air space 81 at the top of the container for enhancing deaeration of the water entering from the ejector 62. A positive means for controlling the water level is shown in FIG. 1 in form of a valve 79 automatically operated to control the flow of the water from the container by a liquid level sensing device generally designated 82. Other well known ways and means may be employed to control the level of liquid in the container 76. In any case, a regulated flow of water from the container to the flash evaporator is provided via conduit 80 and pump 45.

In operation, the low pressure steam is rapidly directed through the ejector 61 and its suction chamber 67 by way of a suction creating nozzle (not shown). The rapid flow of steam through the nozzle creates a suction in the chamber 67 which functions to draw air and other noncondensible gases from the flash evaporator as indicated by the line 71 mentioned above. The line 71 is directly connected to the condensing space 27 of the flash chamber 3 and is indirectly connected to the condensing spaces 26 and 25 of the flash chambers 1 and 2 by way of the previously mentioned orifices 23 and 24 provided in the partitions 17 and 18. e

The low pressure steam and the gases withdrawn from the flash chambers exhaust into the suction chamber 68 of the water actuated ejector 62. The water directed through the suction chamber 68 by the pump 75 creates a suction in the chamber which draws the steam and gases from the ejector 61, and further functions to condense the steam exhausting from ejector 61 which in turn creates a vacuum that augments the vacuum (suction) created by the liquid flow.

From the ejector 62, the actuating water, the air and other gases from the ejector 61, and the condensed steam (condensate) exhaust into the air space 81 provided in the water supply container 76 as indicated by line 83. The air and other non-condensible gases, vent to the atmosphere, as indicated by line 84. The water exhausting from ejector 62 may be sprayed into space 81 to facilitate the liberatlon of entrained gases from the water for the venting thereof to the atmosphere. The water and condensate entering the space 81 drop into the water in the container 76 at the level maintained therein. The actuating liquid for e ector 62, in the embodiment of FIG. 1, is mainly the water stored in the container 76. The water may be withdrawn from the container in a controlled manner, via conduit 80, as explained earlier.

The steam entering the suction chamber 68 of e ector 62 from ejector 61 and condensed by the actuating makeup water flowing through the ejector 62, raises the temperature of the water stored in container 76. A reasonably moderate container water temperature value is obtained, however, with the removal of a portion of the water from the container via valve 79 and line 80 and directed to the heat exchange means 42 and 41 as makeup water by pump 45 and line 48. The makeup water enters the condensing tube structure (via line 46) unheated and thus must be heated by the top heater 49 for the flash evaporation process as explained earlier: The heat transferred to the makeup water in the container is thus eflectively utilized in the flash evaporation process and system since it performs a necessary (heating) function therein while simultaneously providing efiicient cooling of the water stored in the container 76.

FIG. 2 shows another embodiment of the invention employing the staged ejector arrangement in which the makeup or feed Water is employed as the sole actuating liquid for ejector 62 instead of the water stored in the container 76 as used in FIG. 1. In the figures, like numerals refer to like parts. Both ejectors 61 and 62 function in the manner described in reference to the embodiment shown in FIG. 1.

In FIG. 2, as in FIG. 1, the product water is directed from the system directly to storage and/ or consumption, as indicated by line 59. The makeup water is pressurized and directed to the ejector 62, as indicated by line 74, for actuating the ejector and condensing the low pressure steam exhausting from ejector 61 as explained in reference to FIG. 1. The makeup water is directly preheated by the steam entering suction chamber 68 thereby utilizing the acquired heat to aid the heating function performed by the top heater 49 as explained in connection with FIG. 1. However, all of the makeup water that is not directed to the pump is now rejected from the system after having been heated in tube 43.

The makeup water, the condensate (the condensed steam) and the gases issuing from ejector 62 are exhausted into treatment apparatus generally designated 87, where the makeup water and condensate are pretreated with any suitable chemical additive such as sulfuric acid, for example, to provide the makeup liquid with antiscaling characteristics. In the acid treating process (if used), carbon dioxide is formed and is fed into the air space 81 provided in the liquid supply container 76 with the makeup liquid and the other gases received from the ejectors 61 and 62. In air space 81, the treated liquid is deaerated, and the air, carbon dioxide and other noncondensible gases are vented to the atmosphere, as indicated by the line 84. Thus, with the acid treating process, the container 76 functions as an atmospheric decarbonator for the makeup liquid before it is withdrawn therefrom, as indicated by line 88, and directed by the pump 45 to the flash exaporator 10 for flash evaporation.

In both embodiments of the invention (FIGS. 1 and 2), a highly effective air ejector arrangement 60 has 'been disclosed that is particularly adaptable for a flash evaporator since the ejector operating (actuating) fluids (steam and water) are readily available. The arrangement of the present invention further provides a highly effective preheating means for the makeup water directed to the flash evaporator system by first directing the makeup water to the liquid actuated ejector 62 where the heat is acquired. Further, since no high pressure steam is used to actuate the ejectors in the present invention, the pump 75 and container 76 need not be made of costly stainless steel in order to withstand such pressures and provide a corrosive resistant surface; suitable plastic materials may be used instead. Where the temperature of the ejector actuating fluids may require stainless steel (in place of plastic structures), only the ejectors, and the casing and impeller of pump 75 in the embodiment of FIG. 1 would be subjected to this requirement. In the embodiment of FIG. 2, only unheated, i.e. cool makeup liquid is directed through the pump 75 and ejector 62.

Although the invention has been shown and described in conjunction with the purification of saline or other impure water, it will be understood to those skilled in the art that it is not so limited, but is susceptible of variouschanges and modifications without departing from the spirit and scope thereof. More particularly, it may be employed in conjunction with apparatus designed to remove substantially pure solvent from any solution to provide substantially pure solvent and a residual solution enriched with solute. Thus the second ejector 62 may be actuated by the pure solvent or the solution, and the first ejector 61 may be operated by a vapor of such solvent instead of the above-described low pressure steam.

Though the invention has been described with a certain degree of particularity, it is to be understood that the disclosure has been made by way of example only and that changes may be made therein without departing from the scope and spirit of the invention.

What is claimed:

1. A multi-stage flash evaporation system for extracting a substantially pure product liquid from an impure feed liquid comprising,

a plurality of heat exchanging means,

means for passing the feed liquid through the heat exchanging means to heat the feed liquid to a predetermined temperature,

means defining a plurality of chambers for flash evaporating at least a portion of the feed liquid to form condensible vapors,

the chambers each comprising a heat exchanger means and the chambers being staged successively from a first and highest pressure stage to a last and lowest pressure stage and in successive liquid flow communication with each other, the lower pressure stages forming heat recovery stages and the highest pressure stage a heat reject stage,

a staged ejector arrangement for reducing the pressure within the stages by removing air and other noncondensible gases therefrom, comprising a vapor actuated ejector having a suction chamber and an exhaust portion, the suction chamber being connected in fluid communication With the flash evaporating chambers, liquid actuated ejector having a suction chamber, the lower pressure stages forming heat recovery stages and the highest pressure stage a heat reject stage, an entrance portion and an exhaust portion, the suction chamber being connected in fluid communication with the exhaust portion of the vapor actuated ejector,

a container for receiving a supply of the feed liquid,

conduit means connecting the exhaust portion of the liquid actuated ejector to the container,

means including a pump for delivering pressurized feed liquid to the entrance portion of the liquid actuated ejector,

conduit means for directing at least a portion of the liquid from the container to the flash evaporator heat exchanging means of the heat recovery stages, and

conduit means for directing at least a portion of the feed liquid from the system after it is heated in the heat exchange means of the heat reject stage.

2. An ejector arrangement in combination with a multistage flash evaporator system for removing air and other non-condensible gases therefrom, the system being adapted to produce a substantially pure product liquid from an impure feed liquid by the evaporation of the impure liquid, the evaporator system including a plurality of chambers for flash evaporating at least a portion of the feed liquid to form condensible vapors, heat exchanger means in each of said chambers for preheating the impure feed liquid, said chambers being staged successively from a first and highest pressure stage to a last and lowest pressure stage and in successive liquid flow communication with each other, the lower pressure stages forming heat recovery stages and the highest pressure stage a heat reject stage,

a vapor actuated ejector having an actuating fluid entrance portion, a suction chamber and an exhaust portion,

means connecting the suction chamber to the evaporator for directing the air and non-condensible gases from the evaporator to the suction chamber,

a liquid actuated ejector having an actuating liquid entrance portion, a suction chamber and an exhaust portion,

means connecting the exhaust portion of the vapor actuated ejector to the suction chamber of the liquid actuated ejector for directing the gases and vapor thereto,

a container for receiving feed liquid for the evaporator and having a vent for removing non-condensible gases therefrom, said container and vent being effective to deaerate the feed liquid before it it directed to the evaporator,

means connecting the exhaust portion of the liquid actuated ejector to said container,

means including a pump for providing pressurized feed liquid to the entrance portion of the liquid actuated ejector to actuate the same,

said feed liquid being preheated in the liquid actuated ejector by the vapor and gases directed thereto from the vapor actuated ejector,

conduit means for directing at least a portion of the deaerated and preheated feed liquid from the container to the evaporator heat exchange means of the heat recovery stages, and conduit means for directing at least a portion of the feed liquid from the system after it is heated in the heat exchange means of the heat reject stage.

3. The arrangement of claim 2 including:

means for treating. the feed liquid to minimize scaling with attendant formation of gases,

conduit means connecting the exhaust portion of the liquid actuated ejector to the treating means, and

conduit means for directing the treated liquid from the treating means to the container for deaeration of said gases.

4. The system described in claim 1 wherein the pump has intake and outlet portions,

a conduit for supplying the impure feed liquid to the system,

means connecting said conduit to said intake portion of the pump, and

means connecting the outlet portion of the pump to the entrance portion of the liquid actuated ejector.

5. The system described in claim 4 including means connecting the container to the intake portion of the pump so that a portion of the feed liquid in the container can be recirculated through the liquid actuated ejector.

References Cited UNITED STATES PATENTSv 2,501,276 3/1950 Hickman 202-173 X 2,759,882 8/1956 Worthen et a1. 202174 X 2,893,926 7/1959 Worthen et al. .202173 X 3,288,685 11/1966 Kemper et a1. 20311 3,259,552 7/1966 Goeldner 2033 3,119,752 1/1964 Checkovich 202-l73 X FOREIGN PATENTS 8,522 5/ 1964 Great Britain.

1,028,516 5/1966 Great Britain.

OTHER REFERENCES Chemical and Engineering News, 1948 (July), p. 1985. Saline Water Conversion Report (1963), p. 81.

NORMAN YUDKOFF, Primary Examiner F. E. DRUMMOND, Assistant Examiner U.S. Cl. X.R. 

